Hitherto, inorganic photographic materials such as amorphous selenium, selenium alloys, cadmium sulfide and zinc oxide and organic photographic materials represented by polyvinylcarbazole and polyvinylcarbazole derivatives are widely known as electrophotographic photoreceptors.
It is well known that amorphous selenium or selenium alloys have superior properties as electrophotographic photoreceptors and have been put into practical use. However, in producing these materials, a complicated vacuum deposition process is necessary, and further the vacuum-deposited film obtained has a disadvantage in that the film lacks flexibility. Zinc oxide is used as a dispersed photographic material in which zinc oxide is dispersed in a resin, but such material has problems such as a low mechanical strength and cannot be used repeatedly as is.
Polyvinylcarbazoles known as organic photoconductive materials have advantages such as transparency, good film-forming property and flexibility, but polyvinylcarbazoles per se have no photosensitivity in the visible ray region, and cannot be used practically alone. Accordingly, various sensitization methods have been proposed therefor. Although spectral sensitization of polyvinylcarbazole using a sensitizing dye has resulted in expanded spectral sensitivities extending to the visible ray region, a sufficient photographic sensitivity as electrophotographic photoreceptors cannot be obtained, and it still has a drawback in that photo-fatigue is remarkable.
On the other hand, spectral sensitization with an electron acceptor gives rise to electrophotographic photoreceptors having a sufficient photosensitivity, and some of them have been practically used. However, there are still more problems with mechanical strength and durability.
Various extensive studies have been made on photosensitive materials and there are many reports. However, electrophotographic photoreceptors having a superior electric characteristic and a sufficient photosensitivity have not yet been obtained. At present, there are reports about phthalocyanines which show superior electrophotographic characteristics as dispersed photosensitive materials. However, their spectral sensitivity is partial to the long wavelength region, and they have a drawback in that reproduction of red color is inferior.